Nonwoven fabrics comprise filaments or fibers that are consolidated by a means other than traditional textile technologies and may be utilized in a wide variety of applications requiring a wide variety of properties. Generally, nonwoven fabrics differ from traditional textiles in that nonwoven fabrics do not depend upon the interlacing of yarn for internal cohesion, as do traditional textiles. Nonwoven fabrics comprise fibers or filaments that may be natural, man-made or mineral in origin, or mixtures thereof. The fibers or filaments may be deposited in a web, at random, or orientated in specific directions. The web commonly has little or no strength as first laid down and must be consolidated by external mechanical, thermal or chemical means. The structural integrity of the nonwoven fabric is thus obtained by an external consolidation of the fibers and filaments.
Nonwoven webs are typically formed through a variety of processes. One commonly utilized method for forming nonwoven fabric webs is the latex bonded airlaid method. In the latex bonded airlaid method, fibers that are usually short in length are fed into a forming head via an air stream. The fibers travel along with the air stream until they reach a moving wire upon which they are laid down to form a randomly orientated web. A variety of different types of fibers may be utilized in this method, however short fluff pulp fibers (typically 3-12 mm in length sourcing from treated or untreated pulp) are preferred. The latex bonded airlaid method provides fast manufacturing speeds and produces nonwoven fabrics that are useful in absorbent products and filters/filtration. A variation of the latex bonded airlaid method is the multibonded airlaid method in which low melting synthetic fibers are used to consolidate the cellulosic fibers with a low level binder on either face of the web to control dusting. A third method of forming nonwoven fabric webs is the drylaid carded method. The drylaid carded method is a mechanical process in which bales of fibers are mixed and then combed into a web by a carding machine. The drylaid method favors long, crimped synthetic fibers in order to achieve entanglement.
A further method of forming nonwoven fabric webs is the wetlaid method. In the wetlaid method a dilute slurry of water and fibers is deposited on a moving wire screen and systematically dewatered to form the base web. The wetlaid method can be utilized with a broad range of fiber types. The spunlaid method produces fabric webs by extruding molten polymer granules through spinnerets. The filaments are cooled and deposited onto a moving conveyor to form a web. Other web-forming methods include the meltblown method, in which thermoplastic polymer granules are extruded into a high velocity airstream, solidified and broken into a fibrous web and the flashspun method in which a polymer is dissolved in a solvent and sprayed into a collecting vessel. The polymer/solvent mixture is decompressed by passing through spinnerets and the solvent is then flashed off to leave a network of fibers. The web produced by the spunlaid method has some limited structural integrity, but generally not sufficient consolidation to produce a viable fabric.
Typically, drylaid webs, both airlaid and carded, together with wetlaid have little strength in their unconsolidated form and require external chemical, thermal or mechanical consolidation to provide strength. The process and binder of the present invention are primarily utilized in the chemical consolidation process. In the chemical consolidation process a liquid-based bonding agent is applied to the web. The binder is typically an emulsion, produced by the process of emulsion polymerization that contains one or more monomers that are stabilized with water-based surfactants, colloids or both. In practice, water-soluble initiators are added and the monomer polymerizes to produce a dispersion of solid particles in water. The process is exothermic and the water enables heat transfer during the reaction and provides an acceptable carrier for the polymer. In addition to providing consolidation, the binder imparts many other varying properties to the web. For example, the binder may add functionality, such as antimicrobial properties, to the web and it may add properties such as durability, softness or stiffness and color/opacity.
The binder may be applied to the web via various methods. One method of application is the air-spray bonding method in which the binder is fed from a sealed pressurized vessel through a spray boom into spray nozzles that atomize the binder over the web to provide a homogeneous distribution over the fibers. The airlaid air-spray bonding method alternates steps of passing the web through spray nozzles and drying/curing ovens. For airlaid air-spray bonding, the binder is typically diluted to between 10 to about 35% non-volatile content in order to achieve satisfactory atomization. Nonwoven fabrics can be used in the manufacture of cigarette filter tips. Such manufacture is usually undertaken at high speed and the binders must not include ingredients that are prohibited by the regulatory requirements of the country of manufacture. Traditionally, cellulose acetate fibers have been utilized as cigarette filter tips, however these fibers do not always meet all regulatory requirements. Further, cellulose acetate fibers produce inhalable dust during converting that could potentially lead to health and safety issues for the manufacturer. Finally, cellulose acetate fibers are generally not considered to offer sufficient resiliency for the end use application.
For these reasons, it would be advantageous to provide a binder composition and method of application of the binder composition for the manufacture of nonwoven fabrics that would reduce or eliminate the existing disadvantages in the existing processes for manufacturing nonwoven materials for use in cigarette filters. In particular, it would be advantageous to provide a polymer binder and method for applying the binder to consolidate cellulosic fluff pulp fibers, wherein the polymer binder comprises materials that are allowed for use in cigarette filters by the regulatory agencies of many countries.